java实现优先级队列

优先级队列是一种带有优先级的队列，我们约定关键字最小的数据元素具有最高的优先级，且总是排在队首。

在优先级中的数据元素也不仅仅限制在队尾进行，而是顺序插入到合适的位置，以确保队列的优先级顺序。

实现只有在入队的时候和队列又些区别，用到了之前写的结点Node类

队列接口：

package queueTest;

public interface IQueue {
public void clear();

public boolean isEmpty();

public int length();

public Object peek();// 取队首元素

public void offer(Object x) throws Exception;// 入队

public Object poll();// 出队

public void display();
}

优化结点的data类：

package queueTest;

public class PriorityQData {
//结点的data类
public Object elem;//结点的数据元素值
public int priority;//结点的优先级
public PriorityQData(Object elem, int priority) {
this.elem = elem;
this.priority = priority;
}
}

实现IQueue的优先级队列：

package queueTest;

import linearList.Node;

public class PriorityQueue implements IQueue {

private Node front;//队首的引用
private Node rear;//队尾的引用

public PriorityQueue() {
front=rear=null;
}

@Override
public void clear() {
front=rear=null;
}

@Override
public boolean isEmpty() {
return front==null;
}

@Override
public int length() {
Node p=front;
int length=0;
while(p!=null){
p=p.next;
length++;
}
return length;
}

@Override
public Object peek() {
if(front==null){
return null;
}
else{
return front.data;
}
}

@Override
public void offer(Object x) throws Exception {
PriorityQData pn=(PriorityQData)x;
Node s=new Node(pn);//构造数据域为pn的结点
if(front==null){
front=rear=s;
}
else {
Node p=front;
Node q=front;
while(p!=null&&pn.priority>=((PriorityQData)p.data).priority){
q=p;
p=p.next;
}
if(p==null){
rear.next=s;
rear=s;
}
else if (p==front) {
s.next=front;
front=s;
}
else {
q.next=s;
s.next=p;
}
}
}

@Override
public Object poll() {
if(front==null){
return null;
}
else{
return front.data;
}
}

@Override
public void display() {
if(!isEmpty()){
Node p=front;
while(p!=rear.next){
PriorityQData q=(PriorityQData)p.data;
System.out.println(q.elem+" "+q.priority);
p=p.next;
}
}
else {
System.out.println("此队列为空");
}
}

}

测试：

package queueTest;

public class ProcessManagement {

public static void main(String[] args) throws Exception {
PriorityQueue pm=new PriorityQueue();
pm.offer(new PriorityQData(1, 20));
pm.offer(new PriorityQData(2, 30));
pm.offer(new PriorityQData(3, 20));
pm.offer(new PriorityQData(4, 20));
pm.offer(new PriorityQData(5, 40));
pm.offer(new PriorityQData(6, 10));
pm.display();
}

}

输出：

6 10
1 20
3 20
4 20
2 30
5 40